Design Aspects of Aircraft Airworthiness – Presentation by Sofema Aviation Services (SAS) www.sassofia.com
Introduction – Certification of Aircraft, Design, and Production
The Basic Certification requirements for commercial aircraft are to be found in
- ICAO Annex 8 Airworthiness of Aircraft
- ICAO Airworthiness Manual, Part V State of Design and State of Manufacture
Each ICAO contracting state is responsible to establish its own legal framework to implement the internationally agreed standards and recommended practices. (Note that European Countries rely heavily on EASA to support this entire process ā nevertheless, the legal responsibility still sits with each nation-state).
Certification of Aeronautical Product
Procedures for certification of aeronautical products (aircraft, engines, and propellers) should be e published in each state.
Within the European Union, these requirements will be found in Regulation EC Regulation 748/2012 Annex I – Part 21 and its amendments.
Within the United States, the requirements will be found in FAR Part 21.
EASA Part 21 regulations also include procedures for the approval of design organisations (Subpart J) and production organisations (Subpart G). These processes are known respectively as Design Organisation Approval (DOA) and Production Organisation Approval (POA).
Note: The equivalent FAA term is Design Approval Holder (DAH) and Production Approval Holder (PAH).
Holding such approvals is a necessary pre-requisite to achieving product certification.
Technical Codes
Technical Codes (Certification Specifications for EASA) contain the standards which shall be adopted.
The main technical codes to be followed for the design of products for certification are set out below as a list of certification specifications for Europe (EASA) and airworthiness standards for USA (FAA) applicable to different categories of product and environmental consideration.
CS-22 Sailplanes and Powered Sailplanes
CS-23 Normal, Utility, Aerobatic and Commuter Aeroplanes (Part 23 AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES)
CS-25 Large Aeroplanes (Part 25 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
CS-27 Small Rotorcraft (Part 27 AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT)
CS-29 Large0 Rotorcraft (Part 29 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT
CS-31GB CS-31HB (Gas Balloons) (Hot Air Balloons) Part 31 AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS
CS-E Engines (Part 33 AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES)
CS-P Propellers (Part 35 AIRWORTHINESS STANDARDS: PROPELLERS
CS-LSA Light Sport Aeroplanes
CS-VLA Very Light Aeroplanes
CS-VLR Very Light Rotorcraft
CS-34 Aircraft Engine Emissions and Fuel Venting Part 34 FUEL VENTING AND EXHAUST EMISSION REQUIREMENTS FOR TURBINE ENGINE POWERED AIRPLANES
CS-36 Aircraft Noise Part 36 NOISE STANDARDS: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION
Compliance with Certification Specifications
Compliance with these specifications or standards is approached in one of two ways depending on the requirement.
- For structure – No detrimental deformation of the airframe under the loads produced by a given magnitude of manoeuvre.
- For systems – Any catastrophic failure condition must
o Be extremely improbable [1 in 10 minus 9 flight hours]; and
o Must not result from a single failure.
For the safety assessment of aircraft systems, regulations are given in
- EASA CS25.1309 and FAA ARAC draft AC25.1309-1B.
o Useful guidelines for conducting the safety assessment process are also given in ARP4761 [SAE, 1996].
Type-Certification Process – Summary
The process for civil aircraft by which type certification is achieved comprises four basic steps.
See also FAA Order 8110.4C
- Technical Overview and Certification Basis
o The product designer presents the project to the primary certificating authority (PCA) – EASA in EU, FAA in USA – when it is sufficiently mature.
o The certification team and the set of rules (Certification Basis) that will apply for the certification of this specific product type are established.
o In principal this agreed certification basis remains unchanged for a period of five years for an aircraft, three years for an engine.
- Certification Programme
o The Primary Certification Authority (PCA) and the designer define and agree on the means to demonstrate compliance of the product type with every requirement of the Certification Basis.
o At this stage the level of regulatory involvement is proposed and agreed.
- Compliance Demonstration
o The designer has to demonstrate compliance of the aircraft with regulatory requirements: for all elements of the product e.g. the airframe, systems, engines, flying qualities, and performance.
o Compliance demonstration is done by analysis combined with ground and flight testing.
o The PCA will perform a detailed examination of this compliance demonstration, by means of selected document reviews and test witnessing.
Technical Closure and Type Certificate Issue
o When technically satisfied with the compliance demonstration by the designer, the PCA closes the investigation and issues a Type certificate.
o For European-designed aircraft, EASA delivers the primary certification which is subsequently validated by other authorities for registration and operation in their own countries, e.g. the FAA for the USA.
o EASA will validate the FAA certification of US-designed aircraft.
o This validation is carried out under a Bilateral Aviation Safety Agreement (BASA) between the states concerned.
Concerning the Type Certificate
A Type Certificate applies to an aircraft (engine or propeller) of a particular Type Design.
- Every individual aircraft of that type has to gain its own Certificate of Airworthiness C of A which is achieved when it can be shown to conform to the certificated Type Design and is in a condition for safe operation.
- As a general rule civil aircraft are not allowed to fly unless they have a valid C of A.
Organisation approvals, issued under Part 21, are based on
- Regulatory assessment of capability,
- Facilities,
- Manpower,
- Resources and
- Quality Assurance Systems in relation to the tasks undertaken.
o Supporting standards in this respect are AS/EN 9100 and AS/EN9120B
Next Steps
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Tags:
Aircraft, Aircraft Airworthiness, Aircraft Certification, aircraft design, Airworthiness, Annex I, Aviation Quality Assurance, aviation safety, Certification Programme, Certification specifications (CS), Design Approval Holder, Design Organisation Approval (DOA), EASA, EASA Part 21 Subpart J, EC Regulation 748/2012, FAA, ICAO, ICAO Annex 8, Part 21, PCA, Primary Certification Authority, Production Approval Holder, Production Organisation Approval (POA), Subpart G
